Nobody quite knows what to make of the "Five Star movement" in Italy which is emerging as the surprise winner of this week's Sicilian elections. But one thing is for sure: all the traditional parties are terrified of what might happen in the general elections, which will probably be held in spring 2013. This political movement, led by Beppe Grillo – a volcanic comedian with a huge mop of shaggy greying hair – is threatening to tear Italy's political establishment apart.

The rise of the movement has been sudden. In local elections in May 2012, a Five Star representative was elected mayor of Parma, one of Italy's richest cities, which until the late 1990s was a centre-left stronghold, and was then governed (badly and dishonestly) by Silvio Berlusconi's party for more than a decade. And in Sicily, the Five Star movement this weekend gained more votes than any other party and had 15 regional councillors elected. In typical exuberant fashion, Grillo had swum across the Straits of Messina (3km) to launch his campaign.

So, who is Grillo and what is the Five Star movement? The first part is easier to answer. Grillo is 64 years old and from Genoa. He was a popular and clever comedian who starred on Italian TV in the 1970s and 1980s. Then he did something unthinkable: he called Bettino Craxi's Socialist party "thieves" on national television. This led to his banishment for a number of years, and in the meantime Grillo built up a huge audience with a series of ferocious shows across Italy.

For a long time, Grillo was anti-technology: his show would end with him smashing up a computer. But then he embraced the internet. He understood, before almost anyone else in Italy, the political potential of the web and its ability to undercut the country's stifling and boring media monopolies and party-controlled news outlets. Thus, via his incredibly popular blog, and latterly through Twitter, he began to spread a potent anti-political message. This linked up with both a long-running hatred and distrust of politicians among many Italian voters, and the exacerbation of these deeply rooted tendencies during the Berlusconian era (1994-12), a time of almost obscene levels of corruption, patronage, clientelism and cronyism at all levels.

Grillo railed against all this, and he did his homework. He documented absurd levels of state contributions for nonexistent political newspapers, for example, and drew on widespread disgust concerning parliamentary pension rights and payoffs. He attacked both left and right, almost equally. Berlusconi was "a psycho-dwarf", Pierluigi Bersani (the leader of the centre-left Democratic party) was a "zombie" and "Gargamella" (a character from the Smurfs cartoons).

His language was violent and straightforward, and he organised a number of "fuck-off days" of protest against the governing parties (and in fact against all parties). He also attacked big business and called for more shareholder democracy.

When the Five Star movement was formed in 2009, Italy was falling apart: still governed by a moribund Berlusconi government, the country was paralysed by corruption scandals on an almost daily basis, while sliding into a deep recession and financial crisis. Not surprisingly, people stopped voting altogether, or began to abandon the major parties. A bestselling book detailed the grotesque waste perpetuated by a robber class of politicians. Its title was eloquent: La Casta, The Caste.

Grillo's followers, as far as we know, tend to be young and idealistic. Most of his candidates have no political experience. Many, if not all, have grown up with the internet and use it almost exclusively to communicate and obtain information and news. Grillo's party is both postmodern and post-political. But the Five Star movement combines these new elements with old-style, anti-political populism.

Anti-politics has a long history in Italy, going back to fascism itself, and moving through short-lived movements like the Ordinary Man (L'Uomo Qualunque) which briefly emerged in the 1940s. In the 1990s and 2000s, the Lega Nord used a highly successful brand of regionalist populism and gained access to power structures at a national and local level as a result.

What does Grillo's success mean for Italy? It is interesting to look at the Five Star "programme", which is almost entirely negative. The manifesto consists largely of a series of existing laws that will be abrogated on taking power, plus a bit of ecology (Grillo is almost messianic about the environment) and a good dose of euroscepticism. It is not a programme for government. Grillo has nothing at all to say to Italy's 5 million immigrants, and very little to say to Europe. His message is for Italians only, and his violent and anti-institutional language has attracted occasional accusations that he is a "web fascist". Others have seen him as an internet-based version of Berlusconi. There are also questions about his control over the "movement", which appears to be absolute, and perhaps somewhat similar to the power structures that he is so quick to criticise in others.

It may be that the movement will fade and die like so many other populist movements have done. But it could also be true that they are here to stay. Elections are coming up, and the major parties are as unpopular, weak and corrupt as they have ever been. Whatever happens, the Five Star movement can no longer be ignored, and the violent reaction from the political (and intellectual) elite to the rise of Grillo is a clear indication that we need to take this comedian very seriously indeed.